This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The Fe-S cluster of the Rieske protein contains two ligated histidines with the Fe1. The special feature makes it highly possible to involve in not only in the electron transfer, but also in the proton transfer in various kinds of chemical reactions, such as oxidative phosphorylation, photosythesis, biodegradation etc. Since the two histidines are key residues of the redox potential, the pKa of these two are showed to affect the redox potential. Our approach is to watch for the hyperfine shift to get detailed information available exclusively from NMR spectroscopy. In order to know these information, we also need to find ways to assign the two histidines and all the closely related nuclei if they are observable in the spectra. These experiments may be keys to the electron transportation and the proton shuffle in the complex(es).